If a triangle has an angle measuring 90°, what type of triangle is it?

• A. Acute triangle
• B. Obtuse triangle
• C. Right triangle
• D. Equilateral triangle

Answer: (C)

A triangle that has an angle measuring 90° is classified as a right triangle. This is fundamentally based on the definition of triangles and their angles. In geometry, a right triangle is characterized specifically by containing one angle that is exactly 90°. The other two angles in such a triangle are acute, meaning they each measure less than 90°.

This differentiation is crucial for geometry. An acute triangle, for instance, would consist of all angles measuring less than 90°, while an obtuse triangle contains one angle greater than 90°. An equilateral triangle, on the other hand, has all three angles equal to 60°, which also does not fit the definition of having a right angle.

Therefore, identifying a triangle as a right triangle directly stems from the presence of that 90° angle.